The article is dedicated to one of the most important issues of the gas turbine industry – improvement of gas turbine power plant performance, reduction in power consumption for the drive of separate compressors and increase in their productivity through the use of water injection into the compressor. The article provides brief description of a set of parameter calculation programs for the gas turbine power plant performance with compressor-inlet water injection. The complex was developed at St. Petersburg State Polytechnic University. Certain results of the computational study of injection effects on GTK-10 gas turbine are presented to illustrate possibilities of the complex application. The obtained results enable organizing the best option to use injection as for the evaporative cooler during air compression as for the online compressor water wash; and also to control nitrogen oxide emission in exhaust gases. The program, developed by the authors,is tested on a wide range of power characteristics of gas turbines, which are used in full-scale and experimental studies. The calculation results showed good agreement with experimental results.